Electrostatic charge image recorder

ABSTRACT

1,084,494. Television and facsimile picture recording. RANK XEROX Ltd. May 14, 1965 [June 1, 1964], No. 20465/65. Heading H4F. Xerographic apparatus, Fig. 2, for recording television or facsimile pictures comprises a drum 17 bearing a photoconductive layer 56, Fig. 3, supported by a dielectric layer 50 on an earthed conductive member. 51 and, including electrically separate conductors 52, 53, 54 extending parallel to the drum axis. The ends of the conductors 15 engage a brush 13 whereby video signals to be recorded may be applied to successive conductors as, the drum rotates. A light source 31 is traversed back and forth adjacent the drum, the relative rate of traverse and, drum rotation being such the light makes one traverse as each conductor is brought into use. In response to the video signals and the change of conductivity produced in each elemental area by the light source a pattern of charges is created corresponding to the television or facsimile pictures. The charges are developed to a visual pattern by known apparatus 37 and the pattern is thereafter transferred to a record strip under the action of a high potential electrode 44 and fixed thereon by a heater 46. The charge pattern on the drum is then removed by exposure of the drum to an intense light source 25 whilst the electrodes are earthed by brush 20. The electrodes are also earthed by a brush 16 in the region following scanning by light source 31. Conductors 52, 54, 56 &amp;c. may be embedded in dielectric 50 instead of being formed on the surface as shown in Fig. 3. In a modified construction, Fig. 5 (not shown), the earthed conductive member 51 is dispensed with and each of conductors 52, 54 &amp;c. is replaced by two conductors, one of which is earthed. As an alternative to traversing light source 31 back and forth, a scanning light system based on a mirror drum, Fig. 6 (not shown), or rocking mirror may be used. Reference is made (without given details) to a drum system in which the photoconductive layer is removable and forms the base of the final picture. Reference is also made to the application of the invention to a flat bed scanning system.

Feb. 4, 1969 w D H 3,426,354

ELECTROSTATIC CHARGE IMAGE RECORDER Filed June 1, 1964 Sheet of 2 LOCALOSCILLATOR DEMODULATOR 4 50 AMPLIFIER 60 INPUT I AMPLIFIER FIG. 5

INVENTOR. ROBERT W. GUN DLACH BY M 9 9 ATTORNEYS Feb. 4, 1969 R. w.GUNDLACH 3,426,354

ELECTROSTATIC CHARGE IMAGE RECORDER Filed June 1, 1964 Sheet ,2 of 2INPUT AMPLIFIER INVENTOR. ROBERT W. GUNDLACH ATTORNEYS United StatesPatent York Filed June 1, 1964, Ser. No. 371,481 US. Cl. 346-44 Int. Cl.Gtlld 15/06 11 Claims ABSTRACT OF THE DISCLOSURE A xerographic recorderhaving a drum coated with a photoconductive material and having beneathsaid photoconductive material a plurality of parallel signal conductorsseparated from a grounded base conductor by a dielectric material,wherein the signal conductors are closely spaced to each other andextend along the width of the drum and terminate at one end thereof atterminals to which an electrical video signal is applied through a brushpositioned to contact each of the individual terminals as the drumrotates, wherein latent electrostatic images are formed on thephotoconductive material by scanning the surface of the photoconductivematerial along lines corresponding to the lengths of the signalconductors with a scanning spot of constant intensity and by applyingthe video signal through the brush to a signal conductor in the vicinityof the scan, wherein development of the latent image is accomplished bycascading triboelectrically charged toner particles over thephotoconductive material with the developed image thereafter beingtransferred and fused onto a copy sheet, and wherein in anotherembodiment of the drum structure a dielectric material is mountedbeneath the photoconductive material having embedded therein a pluralityof parallel con- This invention relates in general to the conversion ofan electrical signal to a graphic image and, in particular, to a signalrecsorder with electro-optical scanning.

Although there is a great demand today for recorders capable ofproducing graphic reproductions of high speed electrical signalscontaining large amounts of information for applications, such as videorecorders in television or facsimile systems, this demand is stilllargely unsatisfied. This statement is epecially true with regard torelatively fast recording in high quality facsimile receivers. Forexample, in the field of facsimile recording, the receiver may beequipped with either one of the direct recorders now commonly employedin the art or a photo recorder of the type which now finds its greatestuse in news-photo facsimile systems. The direct recording systems forthe most part employ either an electrolytic or an electrosensitiverecording paper. An image is formed on these specially fabricatedrecording papers by causing electrical discharges through very smallsurface areas of the recoding paper which discolor the papers accordingto the magnitude of the applied potential. Since these specially treatedrecording papers may not generally be reused to form a second image,materials cost with this type of recording system is relatively highand, in addition, the discrete nature of the electrical discharges leadsto the formation of a rather crude image formed from a pluralit of smalldiscete dots. Even when poor quality may be tolerated in the finalimage, these systems frequently may not be employed because of theirextremely slow recording speed. Where higher quality or faster recordingis required in facsimile systems, silver halide recording materials aregenerally utilized. However, there are certain disadvantages to thesilver halide photo facsimile recorders which offset their advantages toa large extent. These include the high cost of the silver haliderecording media and the fact that they may not be reused so as toamortize their relatively high cost over a large number of copies, thefact that they must be developed with messy liquid developers undercontrolled conditions and the fact that image access time is relativelyhigh because the images formed are not visible until after development.Instead of using the input signal to cause an electrical discharge onthe recording paper, most photo facsimile recorders employ glow lamprecording or a flying spot scan from a cathode ray tube output. Witheither the glow modulator tube or the cathode ray tube, the light outputis focused on a spot of the recording medium and caused to scan acrossthe recording medium while light intensity is varied according to theamplitude of the signal input.

It is possible to overcome many of the disadvantages of present dayphoto-recorders by substituting xerographic recording for the commonlyutilized silver halide recording technique. Xeography as first describedin US. Patent 2,297,691, and as amplified in many later related patentsgenerally comprises uniformly charging a photoconductive insulatingmember, referred to in the art as a xerographic plate, to sensitize it,and then subjecting it to a light image or other pattern of activatingelectromagentic radiation which serves to dissipate charge inradiation-struck areas, thus leaving a charge pattern or latentelectrostatic image on the photoconductor conforming to theelectromagnetic radiation pattern. Of course, in a facsimile recordingsystem, the whole of the light image would not be exposed to thexerographic plate simultaneously but rather the xerographic plate wouldbe scanned with a light source, the intensity of which is variedaccording to the input signal amplitude. Following exposure, the imageis developed by the deposition of electroscopic or electrostaticallyattractable, finely divided, colored material, referred to in the art astoner, on the exposed photoconductive insulator, which by virtue of itslatent electrostatic image, forms a corresponding toner image on itssurface. The toner image thus formed may then optionally be viewed insitu on the photoconductive insulating layer or transferred to a copysheet such as paper or other material for later use. In the event thatthe xeographic plate employs amorphous selenium as its photoconductiveinsulating layer, as described more fully in US. Patent 2,970,906, toBixby, the toner image may be transferred to a copy sheet and axerographic plate may immediately be cleaned and reused in the processfor many thousands of cycles. In view of the fact that the cost of theselenium xerographic plate may be amortized over the many thousands ofcopies which it is capable of producing, the cost of photosensitivematerials per copy is extremely low as compared with silver halidematerials and the process is still capable of producing photo-exactreproductions of the facsimile originals transmitted from the source.Although the above described xerographic photo-facsimile recorder has anumber of advantages over ordinary silver halide recorders including lowcost, ease of development, fast access time, etc., it is somewhat slowerin photographic speed than the fastest silver halide recordingmaterials.

Accordingly, it is an object of this invention to define a novel methodfor the xerographic recording of video signals.

It is a further objective of this invention to define a novel apparatuscapabie of recording video signals at high speed and low cost.

It is yet another object of this invention to define novel methods andapparatus for the xerographic recording of video images withelectro-optical mixing techniques.

Yet another object of the invention is to provide a xerographicphotorecording method of greatly increased s eed.

The above and still further objects, features, and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed disclosure of specific embodiments of the invention,especially when taken in conjunction With the accompanying drawingswherein:

FIGURE 1 is a partially diagrammatic isometric view of a facsimilereceiver constructed according to this invention, with some of the majorsystem components removed;

FIGURE 2 is a view of the right-hand end of the apparatus seen in FIGURE1 including additional apparatus components not shown in FIGURE 1;

FIGURE 3 is a broken partially sectioned end view of the drumillustrated in FIGURES 1 and 2;

FIGURE 4 is a top sectional view taken along section lines 44 of FIGURE3; and

FIGURE 5 is a broken partially sectioned end view of an alternateembodiment of the drum of FIGURE 3;

FIGURE 6 is an isometric view of an alternative high speed scanningmechanism.

Although this invention is broadly directed to an electricalsignal-to-graphic image converter for the recording of images, afacsimile receiving system has been illustrated in isometric in FIGURE 1as an exemplary illustration of the inventive concept. In this system, afacsimile signal received through a transmission line from a facsimiletransmitter is fed through input lines 10 to a demodulator 11 where itis separated from its carrier frequency prior to being fed into an inputamplifier 12. The input amplifier has its output connected to a smallbrush 13 which is mounted on a stationary support 14. The brush 13 is ofsuch a size and is so positioned that it makes electrical contact witheach successive contact 15 on the insulating end face of a cylindricaldrum generally designated 17 as the drum is rotated about itslongitudinal axis. Since, as is explained in more detail hereinafter,each of the contacts 15 is electrically connected to one of a greatnumber of mutually parallel conductors which are also parallel to thelongitudinal axis of rotation of the drum 17 and imibedded in the drumclose to its outer peripheral face, rotation of the drum at a time whenan input signal is being received by the system causes the input signalto be switched from one very small longitudinal segment near the face ofthe drum to the next. This is perhaps best seen by viewing the conductor5254 in FIGURE 4. In other words, the system is constructed so as tocause the electrical input signal to scan around the drum surface, withthis signal being applied to sequential line segments of the drum facewhich are taken along a line parallel to the drum axis.

The output signal of a very stable local oscillator 18 is fed into anamplifier 19 which in turn is employed to power a synchronous motor 21that is used for mechanically driving the moving parts in the system. Apinion 22 is mounted on the shaft of the synchronous motor 21 and is indriving engagement with another gear 23. Gear 23 is mounted on the shaft24 of drum 17 so that it directly rotates this drum in a directionindicated by the arrow in FIGURE 1. In addition, a large gear 26 is alsomounted for rotation on shaft 24 and is in driving engagement with asmall pinion 27. Pinion 27 is mounted on a shaft 28 in which there hasbeen cut a reversing lead screw and on which there is mounted a carriage29 for traversal back and forth in front of drum 17 as shaft 28 isrotated. Carriage 29 carries a light source 31 and a lens 32 positionedto image light from source 31 on a very small spot on the surface ofdrum 17. Light source 31 may consist of any high intensity, constantoutput light source such as a carbon arc lamp or the like. The abilityto use a constant high intensity light source in this system as opposedto the modulated light sources of other photofacsimile systems is agreat advantage, especially in xerographic systems which generallyemploy materials with rela ively slo P graphic speeds since this allowsfor a great increase in scanning speeds. Internal threading in carriage29 and the extent of the thread cut on shaft 28 are designed so that thespot of light produced b light source 31 and lens 32 on the surface ofthe drum 17 will only traverse that portion of the drum 17 covered by aphotoconductive insulating layer 33. Carriage 29 also contains atriangular hole which is utilized for mounting the carriage on atriangular guide bar 34 which in turn is mounted on a supporting stand35. Although they are not illustrated in this figure so as to simplifythe description of the invention, all shafts, the motor, and stand 35are mounted on suitable rigid stationary supports. As described above,the electrical signal input to the system, after demodulation andamplification, is applied along whole line segments of the drum 17.Since, as will be explained more fully hereinafter, a latentelectrostatic image is formed at the point Where a signal activatedconductor intersects with the spot of light projected on the drumsurface by light source 31 and lens 32, there is, in effect, a scanningacross the drum by this light source and since the strength of thelatent electrostatic image formed is dependent upon the magnitude of theinput signal, the system is perhaps best understood by analogy to acathode ra tube. In this analogy, light source 31, lens 32, theircarriage and traversing mechanism are analogous to the horizontaldeflection plates of a cathode ray tube While the conductors runningthrough the drum are analogous to the electron gun in a cathode raytube. This analogy holds because the scanning light determines where onthe drum the latent electrostatic image will be formed and the signal onthe conductor in the drum determines its strength or intensity. Verticalscanning of the drum is accomplished by its rotation.

It is to be understood, of course, that although the whole of thefacsimile transmitter is not illustrated and described here, that thetransmitter and recorder must be operated in very close synchronism sothat an image which closely corresponds to the original is reproduced inthe recorder. For example, in an exemplary system, the original isplaced on a transmitting drum of the same size as recording drum 17 anddriven with a local oscillator, amplifier, synchronous motor and geartrain identical to that employed in the recorder. A light is placed onthe original copy on the drum and a carriage carrying the light and alens or lens system and p'hototube image the light reflected off a spoton the original copy onto the phototube. This carriage is carried by areversing lead screw similar to, and driven in the same manner as, leadscrew 28 in the recording head. The signal from the phototube is thenfed to a modulator where it is mixed with a carrier frequency from acarrier signal generator, amplified and transmitted either on atransmission line or by radio propagation. If it is desired to keepcosts at a minimum, local oscillators of the same frequency in thetransmitter and the recorder may be dispensed with and the system mayrely for synchronization on the frequency control of the local powerlines. Other synchronization techniques Well known in the art such asemploying the carrier for synchronization may also be employed. Inaddition, it is to be noted that the drive train in the illustratedrecording system is continuous in nature. That is to say the localoscillator 18, amplifier 19, and synchronous motor 21, are in continuousoperation except when manually switched on and off. However, in adetailed showing of a practical system, a phasing system to place thebeginning of a received scanning line at the left-hand edge of therecording would also be included. In that type of a system, although thelocal oscillator, amplifier and synchronous motor are run continuously,a solenoid actuated clutch is included in the mechanical gear train andis actuated by a phase pulse amplifier operated by the system input,

Once the latent electrostatic image is formed on drum 17 by the combinedaction of light 31 and the electrical input signals, it is developed ormade visible and transferrcd to a sheet of recording paper or other copymaterial. Apparatus for accomplishing these developing and transferSteps have not been illustrated in FIG. 1 for simplicity of illustrationof other system concepts; however, in addition to many of the systemcomponents illustrated in FIG. 1, the additional developing and transfersystem components are illustrated in some detail in FIG. 2. Referringnow to FIG. 2, it is seen that once the latent electrostatic image isformed by the combined action of light source 31 and the electricalsignal applied to the drum through brush 13, it passes a grounded brush16, the purpose of which is described hereinafter, and then the drumrotates around so as to move past a developing unit generally designated37. This developing unit is of the cascade type which includes an outercontainer or cover 38 with a trough at its bottom containing a supply ofdeveloping material 39. The developing material is picked up from thebottom of container 38 and dumped or cascaded over the drum surface bynumber of buckets 41 on an endless driven conveyor belt 42. Thisdevelopment technique which is more fully described in US. Patent2,618,552, to Wise and 2,618,551, to Walkup utilizes a two-clementdeveloping mixture including finely divided, colored, marking particles,or toner, and grossly larger carrier beads. The carrier beads serve bothto deagglomerate the toner and to charge it by virtue of the relativepositions of the toner and carrier material in the triboelectric series.When the carrier beads with toner particles clinging to them arecascaded over the drum surface, the electrostatic fields from the chargepattern on the drum pull toner particles off the carrier beads servingto develop the image. The carrier beads along with any toner particlesnot used to develop the image then fall back into the bottom ofcontainer 38 and the developed image moves around until it comes intocontact with a copy web 42 which is pressed up against the drum surfaceby two idle rollers 43 so that the web moves at the same speed as theperiphery of the drum. A transfer unit 44 is placed behind the web andspaced slightly from it between rollers 43. The transfer unitillustrated contains one or more wire filaments which are connected to asource of high potential 45 and operate on the corona dischargetechnique as described in US. Patents 2,588,699, to Carlson, and2,777,957 to Walkup. Essentially, this transfer technique which isdescribed in US. Patent 2,576,047, to Schaffert, consists of spacing thefilaments slightly from the surface to be charged, placing a groundedconductive base behind this surface and applying a high potential to thefilament so that a corona discharge occurs between the filament and thesurface, thus serving to deposit charged particles on the surface. Thepolarity of potential source 45 and consequently the polarity of thecharge deposited on the surface is opposite to that of the charge on thetoner particles employed to develop the drum so that the chargedeposited on copy web 42 serves to attract the toner particles away fromthe surface of the drum. Obviously, this deposited charge must besufiicient to overcome the force of attraction between the particles andthe charge of the latent electrostatic image formed on the drum. Itshould be noted at this point that many other development and/ortransfer techniques known in the xerographic art may be utilized withthis invention. For example, development may be accomplished by magneticbrush development, as described in US. Patent 3,- 015,305, to Hall, orby powder cloud development, as described in US. Patent 2,918,900, toCarlson, and transfer may be accomplished by employing a rollerconnected to a high potential source opposite in polarity to the tonerparticles immediately behind the copy web or the copy web itself may beadhesive to the toner particles. In addition, transfer may beaccomplished by placing a grounded conductive plate behind the copy webat the point of transfer and applying a pulse of the same polarity asthe charge on the toner particles to the conductors in the drum. Thistransfer technique, which is more fully described in my above-referencedapplication, serves to repel the toner particles making up the developedimage off the drum and onto the copy web. After transfer to the copyweb, the web moves beneath a fixing unit 4 6 which serves to fuse orpermanently fix the toner image to web 42. In this case, a resistanceheating type fixer is illustrated; however, other fixing techniquesknown in the xerographic art may also be utilized including thesubjection of the toner image to a solvent vapor or the spraying of thetoner image with an overcoating. A-fter fixing, the web is rewound on acoil 47 for later use. Once past the transfer station, the drumcontinues around and moves into a position where it is exposed to astrong light source 25 while its conductors are grounded through a brush20. This dissipates all charge remaining at the photoconductordielectric interface. The drum then moves beneath a cleaning brush 48which prepares it for a new cycle of operation.

In FIGURE 3, there is illustrated a fragmentary partially sectional endview of one embodiment of the drum structure which my be employed inthis invention. This embodiment comprises a dielectric layer 50 on agrounded conductive backing member 51 which may also act as a rigidsupporting structure for the drum. Over dielectric layer 50 there are anumber of electrically separated conductors 52, 53, 54, etc., which maydesirably run in parallel lines in a direction parallel to the axis ofrotation of the cylinder as seen in FIG. 1. These conductors are veryslender and thin and are uniformly spaced ranging from about 75 to about350 conductors per inch of drum circumference although less or moreconductors per inch may be employed depending upon considerations ofimage quality to be reproduced, cost and the like. The conductors maycover on the order from about 30 to about 70% of the surface area of theunderlying dielectric layer 50. These conductors may be placed on thesupporting dielectric layer 50. These conductors may be placed on thesupporting dielectric layer by means of photoresist and etch orengraving techniques which are well known in the printed circuit arts.It is also to be noted that if desired, the conductors may be embeddedin the face of, or actually buried within dielectric layer 50; however,since the purpose of these conductors is to set up electrical fieldsthrough the uniform layer of photoconductive insulating material 56overlying them, it is preferable that they be placed on the surface ofthe dielectric layer 50.

FIG. 4 is a partial section taken along section lines 4-4 of FIG. 3which cuts through the drum along the top surface of conductors 52, 53,and 54. This section also cuts through the photoconductive insulatinglayer 56 in those portions of the drum which are not covered by theconductors 5254. As shown in FIG. 4, the photoconductive insulatinglayer 56 does not extend the whole width of the drum but only covers aportion of the dielectric base 50. As also shown in this figure, afterthe conductors emerge from the photoconductive insulating film on theright-hand side as seen in the figure, they continue on above insulatinglayer 50 to an insulating end plate 57 which may be fabricated of thesame material as layer 50 and are connected to a number of contacts onthe right-hand surface of plate 57 for commutation with brush 13.

In FIG. 5, there is illustrated a fragmentary partially sectional viewof an alternate embodiment of the drum, the illustration of which issimilar in nature to that of FIG. 3. In this second embodiment, a numberof electrioally separated parallel conductors 59, 60, 61, 62 and 63,similar to conductors 52-54 of FIGURE 3, are embedded in a dielectriclayer 64. This dielectric layer is overcoated with a photoconductiveinsulating layer 66. Preferably, the thickness of the dielectricmaterial 64 between the conductors 59-63 and the photoconductiveinsulating layers 66 is kept quite thin so as to maximize theelectrostatic field which will extend up to the photoconductiveinsulating layer from these conductors upon the application of anelectrical potential to them. In this embodiment of the drum theelectrical input signal from the amplifier is applied across twoadjacent conductors to set up the electrical field necessary to form alatent electrostatic image on the drum. One method for accomplishingthis result is to ground alternate conductors such as 59, 61, and 63,while connecting the conductors between these alternate conductors suchas 60 and 62 to contacts such as 67 on the end face plate 68 of thedrum. Then by grounding one output terminal of the input amplifier andconnecting the other output terminal of this amplifier to brush 13, theoutput signal from the amplifier is applied across two adjacentconductors when brush 13 brushes against the contact 67 for one of thoseconductors.

The photoconductive insulating layer in either the FIG. 3 or FIG. 5embodiment may, for example, consist of amorphous selenium, thexerographic use of which is more fully described in US. Patent2,970,906, to Bixby. Amorphous selenium is, of course, the preferredmaterial for the photoconductive insulating layer of the drum since itproduces excellent copy and is reusable in the process for manythousands of cycles. It is to be noted, however, that any other suitablephotoconductive insulator may also be employed even when they arephotographically slower than amorphous selenium and not reusable shortlyafter light exposure. A prime example of this type of material isparticulate French process zinc oxide in a film- -forming insulatingbinder such as a polystyrene or polyvinyl acetate resin. This type ofphotoconductive insulating layer may, for example, be deposited on adielectric film backing and the recording drum may be provided withgrippers and/ or rollers to hold a cut dielectric sheet with the zincoxide coating against the drum in close proximity to the conductorsduring one cycle of operation. After completion of the cycle, a freshphotoconductive insulating layer may be placed in the system eithermanually or with an automatic feed system in which, for example, thegrippers for the photoconductive insulating layer may be cyclically camactuated. This type of system has the virtue that the transfer step mayhe eliminated from the overall process and the toner image may be fixeddirectly on the surface of the photoconductor.

Although a reversing lead screw scanning mechanism has been described inconnection with FIGURE 1 so as to facilitate the description andunderstanding of the invention, it is to be noted that in actualpractice, higher speed scanning mechanisms are employed to takeadvantage of the fact that the high unmodulated intensity light sourcesutilized with this invention will allow for much shorter scanning times.Such a high speed scanning device is shown in FIGURE 6, and this deviceincludes a light source 74, a lens 76 and an aperture 77, designed tofocus a spot of light on a rotating hexagonal mirror 78, mounted on ashaft 79 which is driven by a synchronous motor drive 80. After passingthrough aperture 77, the light is reflected oif whichever face ofhexagonal minror 78 happens to be opposite the light source at thatparticular time, and is reflected through lens 81 to cylindricalrecording drum 17 of the same type as described in connection withFIGURE 1 above. 60 of rotation of hexagonal mirror 78 causes each mirrorthen opposite the light source to cause the light reflected 01f itssurface to scan from one end of cylindrical drum 17 to the other end asshown by the arrow moving across the drum. As the next mirror face comesopposite the light source, it causes the light to once again scan thedrum so that for each rotation of hexagonal mirror 78, the drum isscanned 6 times from right to left as seen in FIGURE 6. The video signalis applied to the drum in the same manner as described above inconnection with the FIGURE 1 embodiment of the invention and therotational speed of cylindrical drum 17 is adjusted to coincide with thescanning rate of the light source.

In operation, an original copy is placed on the facsimile transmitterdrum and the transmitter is switched on causing the drum to rotate at aspeed determined by the frequency of its local oscillator and thecharacteristics of its synchronous motor. If the scanning head of thetransmitter were tied in with this drum, turning on of the localoscillator at the transmitter would also initiate scanning by thescanning head. As described above, the transmitter scanning headincludes a light source, a lens system, and a phototube pickup sopositioned and arranged as to cause a spot of light from the lightsource to be reflected off the transmitting drum to the phototubepickup. Thus, when the scanning head light strikes a white orlightcolored portion of the original, it reflects a large amount oflight back to the phototube, whereas when this light strikes a dark orblack portion of the original, most of the light is absorbed and verylittle is reflected back to the phototube pickup. Consequently, thepotential appearing at the phototube output is directly proportional tothe lightness or darkness of the particular small elemental area of theoriginal being scanned at any particular time. Since the rate of travelof the scanning head across the drum is high with respect to the speedof rotation of the drum, the whole surface area of the original on thetransmitter drum is scanned one elemental area at a time in aline-by-line fashion. As explained above, the output signal of thephototube is mixed with a carrier frequency and transmitted either overa transmisison line or by radio propagation to the receiver which thendemodulates and amplifies this signal prior to applying it to brush 13.This brush makes electrical contact with one of contacts 15 on the endface of the recording drum 17. The ratio between gear 26, which ismounted on the shaft of the drum 17, and gear 27, which is mounted onthe shaft carrying the lead screw for carriage 29, is selected so thatbrush 13 makes electrical connection with one or several of the contacts15 for a time interval equal to the time required for the scanning spotof light to make one traversal across the full width of thephotoconductive insulating layer 33 on the drum surface. This means thatthe varying electrical input signal is continuously applied to one orseveral of the conductors in the drum as light source 31 on the carriage29 scans across the photoconductive insulating layer 33 directly abovethe activated conductor or conductors.

Referring now to FIG. 3, it is seen that when an electrical signal isapplied to one of the conductors such as 52, 53, or 54, an electricalfield is set up between the conductor and the grounded conductivebacking plate 51 of this drum embodiment. Although some of the fieldlines proceed directly from the bottom of the conductor to theconductive grounded plate 51, other field lines curve up from the top ofthese conductors through the photoconductive insulating layer 56 andthen down through the photoconductive insulating layer between adjacentconductors through the dielectric layer 50 to the grounded conductivebacking layer 51. Whether or not an electrical field is set up in thephotoconductive insulating layer 56 is thus dependent upon whether ornot a signal is applied to one of the conductors 52-54, and itsinstantaneous strength is dependent upon the instantaneous amplitude ofthe electrical signal being applied. If the photoconductive insulatinglayer 56 is not subjected to exposure by light or other Iactivatingelectromagnetic radiation, it will, of course, remain in its mostinsulating condition so that charge carriers within it will have littleor no mobility. On the other hand, if any section of the photoconductiveinsulating layer is exposed to light, the illuminated areas will becomerelatively more conductive. As is well known, an electric field, whenapplied to a conductor, causes the charge carriers within it to move insuch a way as to make the interior of the conductor a field-free,equi-potential volume. For example, if the area of the photoconductiveinsulating layer lying above condoctor 53 in FIGURE 3 were illuminatedso as to render this area relatively conducting, while an electricalsignal were being applied to this conductor from the input amplifier,the electric field resulting from the application of the signal betweenthis conductor and the grounded conductive backing plate 51 would causethe free electrons in this conductive area of the photoconductiveinsulating layer 56 to move toward the grounded plate 51 (assuming thatthe applied signal had a negative polarity). It should be noted,however, that although the charge carriers can move through theilluminated photoconductive insulating layer that they would be stoppedat the interface between the photoconductive insulating layer 56 and thedielectric layer 50 because the dielectric remains in an insulatingcondition regardless of illumination. In this instance, then, negativecharge moving toward backing plate 51 would be stopped at the interfaceof the dielectric and photoconductive insulating layers between adjacentconductors such as 53 and 54, and when illumination is shut off, thesecharges would be trapped at this interface because the photoconductiveinsulating layer then reverts to its insulating condition, therebylimiting charge carrier mobility once more. This trapped charge thensets up its own field after the input is shut off and this field formsthe image which is later developed. It is to be noted that the polarityof charge trapped at the interface is dependent upon the polarity of theapplied signal so that if the signal is negative, negative charge willbe trapped at the photoconductordielectric interface while if the signalis positive, positive charge will be trapped at thephotoconductor-dielectric interface. Each of the small conductors 52-54makes up an individual capacitor in conjunction with the dielectriclayer 50 and a common second capacitor plate 51 so that some charge maybe stored in each of these small capacitors. It is thus seen that theapplication of a signal across the capacitor plate for the purpose oftrapping charge at the photoconductor-dielectric interface will alsoserve to store some charge in each of these small capacitors. In orderto alleviate the problem of this additional stored charge, thesecapacitors are shorted so as to discharge them by connecting themthrough contacts 15 to a grounded brush 16 once the photoconductiveinsulating layer above them has passed out of the range of the lightsource 31 and the required charge has been stored at thephotoconductor-dielectric interface by the signal input.

Since the instantaneous value of the signal received by the recorder isthe electrical analog of the reflectivity of that portion or elementalarea of the original document being scanned by the transmitter, andsince the recorders scanning light source 31 is closely synchronizedwith the transmitters scanning pickup, an electrostatic latent image isformed on the recording drum which exactly corresponds to the image onthe original. In effect, then, light source 31 is a traversing opticalswitch which allows the formation of a latent electrostatic image at thepoint where it has virtual intersection with one of the conductors inthe recording drum providing that conductor is carrying an input signalat that particular time. The latent electrostatic image thus formed isthen developed and transferred to a copy web, as described above.

The drum shown in the FIGURE embodiment of this invention operates in amanner similar to that of the FIGURE 3 drum, except that, instead ofusing a plurality of fine separated conductors in the selenium which areseparated from a common grounded conductive backing plate by adielectric layer, all conductors are imbedded in the dielectric layer sothat they are mutually insulated from each other with alternateconductors being grounded so as to substitute for the conductive backinglayer 51 of the FIGURE 3 embodiment. This alternate conductor groundingmay also be used with the FIGURE 3 device. Operation of this drum is thesame as the operation of the FIGURE 3 drum, the only difference beingthat the electric field produced is initiated completely from within thedielectric layer 64 and extends up into the photoconductive insulatinglayer 66 by virtue of the curved nature of the fringing fields produced.Additional detail on xerographic plates of somewhat similar constructionto the FIGURES 3 and 5 drum may be had in the above-referenced copendingapplication.

It should be recognized that many alternate materials, configurations,and modes of operation may be utilized in connection with the concept ofthis invention. For example, the drum components may be madesubstantially transparent and scanning light exposure may be made fromwithin the drum. The drum itself may be made in the form of a fiat platerather than a cylindrical drum and scanned by linear movement of thisplate with respect to the scanning light source. Instead of scanning thedrum with a light source carried on a carriage driven by a reversinglead screw, a rocking concave mirror may project light from a lightsource onto the drum surface or a rotating hexagonal mirror may beemployed for the same purpose. Other methods of transmission, includingsampling circuits and pulse and coding techniques, may be employed aswell as many other Well-known synchronizing methods. In short, the listof alternatives is virtually endless.

What is claimed is:

1. A transducer for the conversion of an electrical signal to a latentelectrostatic image comprising a photoconductive insulating layer,

a plurality of first electrically separated conductors contiguous tosaid photoconductive insulating layer,

at least one second conductor and a dielectric material,

said second conductor being closely spaced to said first conductors andseparated therefrom by said dielectric material,

said first and second conductors being on a first side of saidphotoconductive insulating layer, a source of high intensityelectromagnetic radiation to which said photoconductive layer issensitive,

means to scan areas of said photoconductive insulating layer on a secondside thereof opposite said successive first conductors with said sourceof electromagnetic radiation, and

means to apply an electrical signal representative of information to berecorded between successive first conductors and adjacent secondconductors while areas of said photoconductive insulating layer adjacentsaid first conductors are being scanned with said electromagneticradiation source.

2. A transducer according to claim 1 in which said first conductors areclose to each other and mutually parallel.

3. A transducer according to claim 1 further including means toelectrically connect said first and second conductors after they havebeen scanned by said electromagnetic radiation source.

4. A recorder for the conversion of electrical signals into visibleimages comprising a photoconductive insulating layer,

a plurality of first electrically separated conductors contiguous tosaid photoconductive insulating layer, said first conductors beingseparated from at least one closely spaced second conductor by adielectric material, said first and second conductors being on a firstside of said photoconductive insulating layer, means to scan areas of asecond side of said photoconductive insulating layer opposite said firstside, said scan covering portions corresponding to the length ofsuccessive first conductors, with a high intensity source ofelectromagnetic radiation to which said photoconductive insulating layeris sensitive,

means to apply an electrical signal representative of information to berecorded between successive first conductors and an adjacent secondconductor while portions of said photoconductive insulator adjacent saidfirst conductors are being scanned with said electromagnetic radiationsource,

means to interconnect said first and second conductors after thecompletion of scanning, and

means to deposit finely divided electroscopic marking particles on saidphotoconductive insulating layer whereby the latent electrostatic imageformed on said photoconductive insulating layer is made visible.

5. An image recorder according to claim 4 further including means totransfer the visible image made up of said deposited electroscopicmarking particles from said photoconductive insulating layer to anothersurface.

6. An image recorder according to claim 5 further including means todischarge any residual electrostatic charge remaining on saidphotoconductive insulating layer after a particulate image has beentransferred whereby said recorder is prepared for reuse.

7. An image recorder according to claim 6 in which said discharge meanscomprises means to ground said first and second conductors and means tosimultaneously uniformly expose said photoconductive insulating layer toa source of electromagnetic radiation to which it is sensitive.

8. A transducer for the conversion of an electrical signal to a latentelectrostatic image comprising a photoconductive insulating layer,

a plurality of first mutually parallel, electrically separated,conductors contiguous to said photoconductive insulating layer,

at least one second conductor and a dielectric material, said secondconductor being closely spaced to said first conductors and separatedfrom said first conductors by said dielectric material,

said first and second conductors being on a first side of saidphotoconductive insulating layer,

a source of high intensity electromagnetic radiation to which saidphotoconductive layer is sensitive,

means to scan the side of said photoconductive insulating layer oppositesaid first and second conductors with said electromagnetic radiationalong a line which corresponds to one of said mutually parallelconductors,

means to advance the point of scanning radiation impingement a distanceequal to the distance between adjacent first conductors each time thescanning line completes one traversal of said photoconductive insulatinglayer, and

means to apply an electrical signal corresponding to information to berecorded to a first conductor adjacent to the area of thephotoconductive insulating layer being scanned.

9. A transducer according to claim 8 in which said photoconductiveinsulating layer is in the form of a cylinder, and said means to advancethe point of scanning light impingment comprises means to rotate saidcylinder about its longitudinal axis and said means to scan saidphotoconductive insulating layer in a direction parallel to said firstconductors comprises means to cause traversal of scanning radiationimpingement along the cylinder surface in a direction parallel to thelongitudinal axis of said cylinder.

10. A transducer according to claim 9 in which said means to apply anelectrical signal corresponding to information to be recorded to theconductor above Which the scanning radiation impinges comprises aplurality of electrical contacts on the end face of said cylinder, eachof said electrical contacts being connected to only one of said firstconductors, insulating means to maintain mutual electrical separationbetween all of said contacts and a stationary brush adapted to makecontact with only one of said contacts during one traversal of saidscanning light.

11. An electrical signal to latent electrostatic image transducercomprising a photoconductive insulating layer,

a plurality of first, electrically separated, elongated conductorscontiguous to said photoconductive insulating layer,

at least one second conductor and a dielectric material, said secondconductors being on the same side of said photoconductive layer as saidfirst conductors and being slightly spaced from said first conductors bysaid dielectric material,

a source of high intensity electromagnetic radiation to which saidphotoconductive layer is sensitive,

means to scan along the length of areas of said photo conductiveinsulating layer adjacent to successive first conductors on its sideopposite said first and second conductors with said source ofelectromagnetic radiation, and

means to apply an electrical signal representative of information to berecorded between successive first conductors and an adjacent secondconductor While areas of said photoconductive layer adjacent the lengthof said successive first conductors are 'being scanned with saidelectromagnetic radiation source.

References Cited UNITED STATES PATENTS 3,288,602 11/1966 Snelling 96-13,062,956 11/1962 Codichini 346-74 3,090,828 5/1963 Bain 346-743,199,086 8/1965 Kallmann 178-66 3,301,947 l/1967 Stone 346-74 3,308,2333/1967 Button 178-66 3,308,234 3/1967 Bean 178-66 STANLEY M. URYNOWICZ,JR., Primary Examiner.

L. .T. SCHROEDER, Assistant Examiner.

US Cl. X.R. 178-66

